Rotational coherence spectroscopy of benzene by femtosecond degenerate four-wave mixing

Abstract

Femtosecond time-resolved non-resonant degenerate four-wave mixing (fs-DFWM) experiments were applied to study the rotational coherences in benzene molecules in the gas phase at room temperature. The experiments were performed in a cell filled with benzene vapour at reduced pressure (0.01 bar). The technique gives an excellent signal-to-noise ratio for the observed transients. For the first time transients up to a maximum time delay of 1.4 ns, mainly limited by collisional dephasing, have been obtained for a molecule of this size by fs-DFWM. From this data the rotational constant B = 0.18972 ± 0.00010 cm⁻¹ for benzene at room temperature is obtained by a fitted simulation. The application of fs-DFWM to large molecules seems to be possible and might produce some interesting results in the future.